Acquired performance is not merely a direct reflection of te associative strength of elucidating stimuli. Research using Pavlovian conditioning has demonstrated that other cues present during testing can modify the behavioral impact of eliciting stimuli. We propose to investigate properties of behavioral modifiers called 'occasion setters.' which appear to work by informing the subject of whether or not a subsequent conditioned stimulus is going to be reinforced on that trial. Limited recent evience has suggested that rules for processing of information about occasion-setting are similar to those for simple Pavlovian conditioning. As considerable knowledge of processes governing Pavlovian conditioning already exists, we propose to extend this analogy by seeking additional parallels in occasion setting to well establish Pavlovian processes, thereby further illuminating the nature of occasion setting. Although occasion setting and simple conditioning possible obey parallel rules, evidence suggests that a stimulus's occasion- setting attributes and its Pavlovian excitatory attributes are independent. That is, changing either Pavlovian or occasion-setting attributes of a stimulus does not appear to alter the stimulus' occasion-setting or Pavlovian attributes, respectively. We have demonstrated modulation of the meaning of occasion setters by what we call secons- and third-order occasion setters, and we now propose to investigate the independence of simple excitatory conditioning, first- order occasion setting, and second-order occasion setting. We anticipate both transfer and blocking will occur within a common level of behavioral control, but not between levels of control. Additional studies will examine the role of occasion setting in instrumental discrimination tasks and sequence learning, and the value of hierarchical memory models in explaining occasion setting.